Phase diagram of CuInP2S6 across wide temperature and pressure ranges

Abstract

CuInP2S6 (CIPS) exhibits significant potential for applications in high-integration ferroelectric devices, due to its van der Waals layered structure, which features dangling-bond-free surfaces and maintains room-temperature ferroelectricity down to nanometer-scale thicknesses. A key limitation to its practical application is its moderate polarization strength. This study reports the polarization evolution of CIPS across a wide range of temperatures and pressures and elucidates the mechanisms underlying polarization enhancement under various conditions. The polarization enhancement observed under high-pressure-high-temperature conditions is attributed to the increased occupancy of Cu ions at out-of-plane (CuO) sites, which correspond to high-polarization configurations. In contrast, the high-pressure-low-temperature polarization improvement stems from enhanced ordering of Cu ions. Furthermore, a phase diagram of CIPS over a wide range of temperatures and pressures was established based on Raman spectroscopy and ferroelectric polarization measurements. This diagram further illustrates dipole ordering and Cu-ion freezing in the low-temperature Cc phase. This work provides valuable insights into the thermodynamic and kinetic manipulation of ferroelectric polarization via stress engineering, offering both foundational principles and a deeper understanding of two-dimensional van der Waals ferroelectrics and their potential applications.